--- a/devtools/client/debugger/test/mochitest/browser_dbg_sources-webext-contentscript.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_sources-webext-contentscript.js
@@ -5,17 +5,17 @@
 
 /**
  * Make sure eval scripts appear in the source list
  */
 
 const ADDON_PATH = "addon-webext-contentscript.xpi";
 const TAB_URL = EXAMPLE_URL + "doc_script_webext_contentscript.html";
 
-let {getExtensionUUID} = Cu.import("resource://gre/modules/Extension.jsm", {});
+const {WebExtensionPolicy} = Cu.getGlobalForObject(Cu.import("resource://gre/modules/Extension.jsm", {}));
 
 function test() {
   let gPanel, gDebugger;
   let gSources, gAddon;
 
   let cleanup = function* (e) {
     if (gAddon) {
       // Remove the addon, if any.
@@ -27,20 +27,20 @@ function test() {
     } else {
       // If no debugger panel was opened, call finish directly.
       finish();
     }
   };
 
   return Task.spawn(function* () {
     gAddon = yield addTemporaryAddon(ADDON_PATH);
-    let uuid = getExtensionUUID(gAddon.id);
+    let {mozExtensionHostname} = WebExtensionPolicy.getByID(gAddon.id);
 
     let options = {
-      source: `moz-extension://${uuid}/webext-content-script.js`,
+      source: `moz-extension://${mozExtensionHostname}/webext-content-script.js`,
       line: 1
     };
     [,, gPanel] = yield initDebugger(TAB_URL, options);
     gDebugger = gPanel.panelWin;
     gSources = gDebugger.DebuggerView.Sources;
 
     is(gSources.values.length, 2, "Should have 2 sources");
 

--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -216,23 +216,16 @@ var UUIDMap = {
 
   remove(id) {
     let map = this._read();
     delete map[id];
     this._write(map);
   },
 };
 
-// This is the old interface that UUIDMap replaced, to be removed when
-// the references listed in bug 1291399 are updated.
-/* exported getExtensionUUID */
-function getExtensionUUID(id) {
-  return UUIDMap.get(id, true);
-}
-
 // For extensions that have called setUninstallURL(), send an event
 // so the browser can display the URL.
 var UninstallObserver = {
   initialized: false,
 
   init() {
     if (!this.initialized) {
       AddonManager.addAddonListener(this);